Abortion epidemic in a dairy herd associated with horizontally transmitted Neospora caninum infection

Combined control evaluation for Neospora caninum infection in dairy: Economic point of view coupled with population dynamics

Neospora caninum infection is regarded as one of the most important infectious causes of abortion in dairy cattle. To intervene in its spread, four potential controls including test-and-cull, medication, vaccination, and selective breeding are considered and assessed in this study. The cost of each control, together with the inevitable annual loss due to population dynamics, is adopted as an assessment criterion from an economic point of view. By performing simulation and sensitivity analysis, our results demonstrate that compared with each single control, combined controls are worthwhile with better financial outcomes. For farm affected with significant prevalence (equal to or greater than 30%), vaccine treatment is the most effective and economical option among all control strategies. On the other hand, for farm where prevalence is relatively low (around 10%), combined control, by applying vaccination followed with test-and-cull, medication or selective breeding, could be alternative treatment to provide better financial outcome against single control in an observed period.

Activity of several kinds of drugs against Neospora caninum

Neosporosis caused by Neospora caninum is a serious disease in cattle and dogs worldwide. It is the major cause of abortion and neonatal mortality in cattle. In this study, we evaluated the anti-N. caninum activity of Chinese medicine extracts (curcumin, artemether), herbicides (atrazine, glyphosate), anticoccidiosis drugs (toltrazuril and ponazuril), cyclophosphamide, diminazene aceturate and praziquantel in vitro using parasite growth, replication and host cell invasion assays in human foreskin fibroblast cultures. Curcumin, artemether, atrazine, toltrazuril and ponazuril exhibited inhibitory activity with 50% growth inhibitory concentration (IC50) of 1.1±0.4, 1.0±0.05, 11.2±2.7, 30.3±2.0 and 33.3±4.1μg/ml, respectively, in the growth inhibition assay. They were also active against protozoa replication, but only curcumin was effective against host cell invasion. Glyphosate, cyclophosphamide, diminazene aceturate and praziquantel were ineffective. In an in vivo infection model, curcumin showed no activity against N. caninum infection. We showed that curcumin, artemether, atrazine, toltrazuril, and ponazuril exhibited anti-N. caninum activity in vitro, providing important information for further studies on anti-N. caninum drugs.

What is the global economic impact of Neospora caninum in cattle - the billion dollar question

Neospora caninum is regarded as one of the most important infectious causes of abortions in cattle worldwide, yet the global economic impact of the infection has not been established. A systematic review of the economic impact of N. caninum infections/abortions was conducted, searching PubMed with the terms 'cattle' and 'Neospora'. This yielded 769 publications and the abstracts were screened for economically relevant information (e.g. abortion prevalence and risk, serological prevalence). Further analysis was restricted to countries with at least five relevant publications. In total, 99 studies (12.9%) from 10 countries contained data from the beef industry (25 papers (25.3%)) and 72 papers (72.8%) from the dairy industry (with the remaining two papers (2.0%) describing general abortion statistics). The total annual cost of N. caninum infections/abortions was estimated to range from a median US $1.1 million in the New Zealand beef industry to an estimated median total of US $546.3 million impact per annum in the US dairy population. The estimate for the total median N. caninum-related losses exceeded US $1.298 billion per annum, ranging as high as US $2.380 billion. Nearly two-thirds of the losses were incurred by the dairy industry (US $842.9 million). Annual losses on individual dairy farms were estimated to reach a median of US $1,600.00, while on beef farms these costs amounted to just US $150.00. Pregnant cows and heifers were estimated to incur, on average, a loss due to N. caninum of less than US $20.00 for dairy and less than US $5.00 for beef. These loss estimates, however, rose to ∼US $110.00 and US $40.00, respectively, for N. caninum-infected pregnant dairy and beef cows. This estimate of global losses due to N. caninum, with the identification of clear target markets (countries, as well as cattle industries), should provide an incentive to develop treatment options and/or vaccines.

Detection ofNeospora caninumin aborted bovine fetuses and dam blood samples by nested PCR and ELISA and seroprevalence in Beijing and Tianjin, China

Neospora caninuminfection is a significant cause of abortion in cattle. We investigated the tissue distribution ofN. caninumin aborted bovine fetuses and dam blood samples by a nested PCR assay, and compared the nested PCR with ELISA in the diagnosis ofN. caninuminfection. In total, 26 aborted fetuses and 813 blood samples were collected from 8 dairy herds in Beijing (n=212) and Tianjin (n=601), China. Fifteen fetuses (57·7%) were testedN. caninum-positive by the nested PCR.N. caninumDNA was detected from the brain of 52%, kidneys of 22%, skeletal muscle of 18%, and heart of 4% of the aborted fetuses. The PCR-positive cases (55%, 11/20) were higher than seropositive cows (40%, 8/20) in a subset of 20 fetuses, but the PCR results of blood samples of the 20 cows were all negative. The seroprevalence of the 813 samples was 15·5% (43·4% of samples from Beijing, 5·7% of samples from Tianjin), compared to the PCR-positive blood samples of 0·9%. Our study showed that the nested PCR is a valuable diagnostic tool for the primary diagnosis ofN. caninumin aborted fetuses, while ELISA is the preferred assay for testing blood samples collected from cows. The two assays are complementary in determining whether abortions are associated withN. caninuminfection in cattle.

Neospora caninum in cattle: experimental infection with oocysts can result in exogenous transplacental infection, but not endogenous transplacental infection in the subsequent pregnancy

Whilst it is presumed that infection of pregnant cattle with Neospora caninum oocysts can provoke abortion and is the likely cause of epidemic abortion outbreaks, only two previous experiments have involved inoculation of pregnant cows with oocysts (and only one abortion was provoked in 22 pregnancies). Here, we describe the oral oocyst challenge of 18 cows synchronously bred and inoculated precisely at 70 (n=6), 120 (n=6) and 210 (n=6) days in pregnancy with a nominal dose of 40,000 oocysts. Only one abortion occurred (at the 120 days challenge) which could be definitively ascribed to N. caninum and no transplacental infection (TPI) was detected in any of the other 11 calves born in the 70 and 120 day challenge groups. In contrast, 4/5 live calves born to cattle challenged at 210 days were transplacentally infected. When cows which had transplacentally infected their calves in the first pregnancy were rebred, no TPI occurred. The results show that the timing of challenge influences clinical and parasitological outcomes and that cattle in late pregnancy are exquisitely sensitive to oocyst challenge leading to exogenous TPI and congenitally infected calves. However, cattle which were indisputably systemically infected in their first pregnancy did not induce endogenous TPI in their subsequent pregnancy. This confirms previous results with experimental tachyzoite challenge and suggests that post-natal infection does not lead to persisting infections which can recrudesce in pregnancy.

Prevention of lethal experimental infection of C57BL/6 mice by vaccination with Brucella abortus strain RB51 expressing Neospora caninum antigens

Bovine abortions caused by the intracellular protozoal parasite Neospora caninum are a major concern to cattle industries worldwide. A strong Th1 immune response is required for protection against N. caninum. Brucella abortus strain RB51 is currently used as a live, attenuated vaccine against bovine brucellosis. Strain RB51 can also be used as an expression vector for heterologous protein expression. In this study, putative protective antigens of N. caninum MIC1, MIC3, GRA2, GRA6 and SRS2, were expressed individually in B. abortus strain RB51. The ability of each of the recombinant RB51 strains to induce N. caninum-specific immunity was assessed in C57BL/6 mice. Mice were immunised by two i.p. inoculations, 4 weeks apart. Five weeks after the second immunisation, spleen cells from the vaccinated mice secreted high levels of IFN-gamma and IL-10 upon in vitro stimulation with N. caninum whole cell lysate antigens. N. caninum-specific antibodies of both IgG1 and IgG2a subtypes were detected in the serum of the vaccinated mice. Mice in the vaccinated and control groups were challenged with 2 x 10(7)N. caninum tachyzoites i.p. and observed for 28 days after vaccination. All unvaccinated control mice died within 7 days. Mice in the MIC1 and GRA6 vaccine groups were completely protected while the mice in the SRS2, GRA2 and MIC3 vaccinated groups were partially protected and experienced 10-50% mortality. The non-recombinant RB51 vector control group experienced an average protection of 69%. These results suggest that expression of protective antigens of N. caninum in B. abortus strain RB51 is a novel approach towards the development of a multivalent vaccine against brucellosis and neosporosis.

Associations between Neospora caninum specific antibodies in serum and milk in two dairy herds in Scotland

The study evaluated the use of the Mastazyme ELISA for quantification of Neospora caninum (N. caninum) specific IgG in bovine milk and examined the relationship between serum and milk antibodies in two dairy herds. The serum and milk antibodies both had bimodal distributions in each herd. This was mainly due to between cow variation: in both herds, approximately two thirds of cows were either clearly and consistently seropositive or seronegative for N. caninum with one third consistently near the threshold. Milk and serum N. caninum IgG were strongly related. This relationship was modelled using a linear mixed model including a polynomial term for serum, the effect of herd, and between and within cow variance components. The latter gave a significantly better fit to the data than a model that allowed for a different relationship for the positive and negative (according to the serum test) groups of observations. The sensitivity and specificity (based on serum percentage positivity (pp)) of the milk antibody was determined for different milk pp thresholds. In spite of the differences between the relationship of milk to serum seen for the two herds, for those estimates with sufficient precision, sensitivity and specificity greater than 0.73 for both herds were obtained using single thresholds of 14 and 15.5 for milk pp in both herds based on, as our gold standard, serum antibody pp thresholds of 22.5 and 25, respectively. If milk antibody is to be used for detecting persistently infected cows, the higher threshold of 15.5 may be suitable while for epidemiological screening 14 would be preferable. Further validation in a greater number of herds is required, but our results suggest that this test may prove to be a useful adjunct to serum N. caninum IgG assays in the monitoring of N. caninum infection as part of herd health programmes and epidemiological studies.

Herd-level risk factors for Neospora caninum seroprevalence in dairy farms in southern Brazil

A cross-sectional study was used to test the relationship between herd seroprevalence to Neospora caninum and various potential herd-level risk factors in 60 dairy farms located in two distinct regions in southern Brazil. Thirty farms were randomly selected from within each region. A questionnaire was designed to summarize each farm's production system as it might relate to N. caninum transmission. The questionnaire contained 105 closed questions relating to general characteristics of the farms, farm facilities, management, source of food and water, herd health, environment and biosecurity, which included questions relevant to N. caninum transmission, including presence and number of dogs and other animals, purchase of animals and contact with man. Serum samples were collected from 40% of animals in each farm and N. caninum antibodies were detected by immunofluorescent antibody test (IFAT). The association between potential risk factors and the probability of an animal being seropositive was modeled using a generalized estimation equations (GEE) logistic regression model. The model accounted for multilevel correlation of data from multiple animals within herds. The mean (+/-S.D.) number of animals in the 60 herds was 64.5 (+/-45.6), ranging from 20 to 280 females. Blood samples were collected from 1549 animals. The size of the farms varied from 4 to 100 ha (mean 30.1+/-25.9 ha). At least one dog was found in 57 of the 60 dairy farms (95%). The mean number of dogs was 3.1 (+/-1.9), ranging from 0 to 10. All females were raised on pasture. For all cattle sampled, N. caninum seroprevalence was 17.8%. Overall, 93.3% of herds (56/60) had at least one seropositive animal identified. Four variables were significantly associated with N. caninum sero-response in the 57 dairy farms, which were included in the final multivariable model: the number of dogs on the farm, farm area (hectares), feeding pooled sources of colostrum and region. The odds of a cow being seropositive increased 1.13 times for each additional dog present on the farm (P=0.021). Cattle from farms that fed calves colostrum pooled from multiple cows had 1.79 times greater odds for being seropositive for N. caninum (P<0.003). The probability of being seropositive was inverse to the area of the farms, such that cattle had 0.92 times the odds to be seropositive (P=0.014) for each additional 10 ha of farmland. Finally, cattle from farms in region one had 0.71 times the odds to be seropositive than cattle from region two (P=0.035). Results of this study suggest that several risk factors may explain why dairy cattle in Brazil may become exposed to N. caninum. However, further investigation of these factors is necessary because the purpose of this study was to refine and generate hypotheses on N. caninum transmission.

An abortion storm in cattle associated with neosporosis in Taiwan

An abortion storm associated with acute neosporosis involving 18 cattle was observed in a dairy farm in Taiwan. Aborted fetus age ranged from 3 to 8 months. Of the 38 cattle in that farm examined during the abortion storm, 52.6% (20/38), 13.2% (5/38) and 10.5% (4/38) contained both IgG and IgM, only IgG and only IgM antibodies to Neospora caninum, respectively. No antibody to N. caninum was detected prior to the abortion storm. Follow-up study conducted a year later showed that 23 out of 28 cattle had sero-converted. Since some cattle were positive to either only IgG or IgM, we suggest that both IgG and IgM should be tested for diagnosing neosporosis. Neosporosis surveillance of naive cattle herd is recommended.